Summary. These are the basic steps to having a website hosted through WordPress.com for about $12 per year. Read more about WordPress.com hosting on their Domain Mapping page.
1. Setup a free blog at WordPress.com
2. Pay WordPress.com for domain redirection to your WordPress blog ($12 / year). This is found under Settings > Domains
3. If you have an existing domain/website, login to your host or domain name registrar and change the name servers to be NS1.WORDPRESS.COM, NS2.WORDPRESS.COM, and NS3.WORDPRESS.COM (use up to three if available or only two if that’s all your name registrar offers). [more]
4. Wait up to 24 hours until the domain change propagates and begins forwarding people to the WordPress.com blog you setup.
5. Change the default domain to the .com or .org that you’ve migrated. This is done in your WordPresss.com blog Settings > Domains area from the WordPress Dashboard.